Asbecasite: crystal structure refinement and crystal chemistry

The crystal structure of antimonian asbecasite in an ejectum of hypabyssal origin occurring at Tre Croci near Vetralla, Vico volcanic complex, Roman potassic province, Latium, Italy, has been refined to R = 0.042, and is compared to the original crystal structure determination carried out on the Sb-free asbecasite of hydrothermal metamorphic origin from the type-locality, Cherbandung in Binna valley, Monte Leone nappe, Switzerland. New electron microprobe analyses of samples from both localities demonstrate crystal-chemical features that permit distinction between asbecasites from the two occurrences, so far the only known localities for this mineral.